1. Field of the Invention
The present invention relates in general to a fluid-filled elastic mount which exhibits a high vibration damping effect based on flows of a highly viscous fluid contained therein. More particularly, the present invention is concerned with improvements in such a fluid-filled elastic mount which is capable of effectively damping input vibrations applied in both axial and radial directions of the mount.
2. Discussion of the Prior Art
There is known a vibration-damping cylindrical elastic mount of a type which is interposed between two members in a vibration transmitting system, for flexibly or elastically connecting these two members. The elastic mount has an inner and an outer sleeve which are disposed coaxially or eccentrically with each other, and an elastic body which are interposed between these sleeves for elastic connection thereof. For example, this type of elastic mount is suitably used as a body mount, member mount, engine mount, differential mount, or suspension bushing for a motor vehicle.
The conventional vibration-damping elastic mount constructed as described above relies only upon elastic deformation of the elastic body for damping vibrations applied thereto. Although in recent years there are increasing requirements for elastic mounts capable of more effectively damping or isolating noises and vibrations encountered in a motor vehicle, the conventional elastic mount is unsatisfactory in its vibration damping or isolating capability. At present, there is proposed a so-called fluid-filled cylindrical elastic mount having a fluid chamber or chambers which is/are filled with a suitable fluid, so that the elastic mount can exhibit improved damping or isolating characteristics.
An example of such a fluid-filled elastic mount is disclosed in laid-open Publication No. 62-288742 of unexamined Japanese Patent Application which is assigned to the assignee of the present application. The elastic mount disclosed in this publication has a fluid chamber which is formed between the inner and outer sleeves connected by the elastic body, and which is filled with a highly viscous fluid. In this fluid chamber, there is accommodated a flow-restricting block having external dimensions which are smaller by predetermined values than corresponding internal dimensions of the fluid chamber, so that a flow-restricting portion is formed around the flow-restricting block so as to permit the highly viscous fluid to flow therethrough when vibrations are applied between the inner and outer sleeves.
When a vibrational load is applied to the fluidfilled elastic mount described just above, shearing stresses are applied to masses of the highly viscous fluid existing in the flow-restricting portion of the fluid chamber, whereby the elastic mount is capable of exhibiting relatively high vibration damping characteristics which are not obtained by the conventional elastic mount which utilizes only elastic deformation of an elastic body for damping the input vibrations. Further, the fluid-filled elastic mount is capable of damping vibrations applied in the axial direction of the mount as well as those applied in the radial direction perpendicular to the axis of the mount, based on the fluid flows in the flow-restricting portion of the fluid chamber.
In the fluid-filled cylindrical elastic mount as described above, however, the highly viscous fluid is less likely to flow in the flow-restricting portion of the fluid chamber when the vibrations ar applied in the axial direction of the mount, than when the vibrations are applied in the radial directions of the mount. Therefore, an axial clearance between the axially opposite end faces of the flow-restricting block and the axially opposed inner walls of the fluid chamber should be set to a sufficiently small value, so that the mount can exhibit a sufficient effect of damping the vibrations applied in the axial direction of the mount. In this case, however, the elastic mount tends to have an unfavorably increased dynamic spring constant with respect to the input vibration applied in the radial directions perpendicular to the axis of the mount, due to the excessive flow restriction of the fluid in the flow-restricting portion of the fluid chamber. Accordingly, the known elastic mount is difficult to provide an effective damping effect with respect to the vibrations applied in the axial direction of the mount, while assuring sufficient damping and isolating characteristics with respect to the vibrations applied in the radial directions perpendicular to the axis of the mount.